The present invention relates to a refractory ceramic stopper of the type employed to close, i.e. stop or plug, a discharge opening in a metallurgical vessel. The present invention also is directed to a stopper rod apparatus to be locked to the stopper with the stopper fitting over a stopper rod, thereby to support and enable movement of the stopper relative to the metallurgical vessel and the discharge opening thereof. The present invention also relates to an assembly of such stopper and such stopper rod apparatus.
Devices of this general type are known, for example as disclosed in European EP 0 358 353 A2. In such known system, a refractory ceramic stopper has built thereinto a metallic coupling having internal threads. A stopper rod having an outer thread can be screwed into the metallic coupling in the stopper. As a result, the stopper is mounted on the stopper rod. However, this known arrangement has a number of disadvantages.
For example, when the stopper is manufactured, the metallic threaded coupling therein is subjected automatically to the firing temperature for manufacture of the stopper, for example 1350.degree. C. During such firing, the threaded metallic coupling can become oxidized. Cracks also can be formed due to the different coefficients of thermal expansion of the ceramic material of the stopper and the metal material of the threaded coupling. All such occurrences have a negative impact on the function and operation of the threaded coupling.
Also in this known system, the thread of the threaded coupling and the thread of the stopper rod must be complementary to each other. As a consequence, when a given installation already has an existing stopper rod, then only stoppers having threaded couplings with precisely matching threads can be employed with such already existing stopper rod. Therefore, when there exist a number of stopper rods having varying threads, it is necessary to provide availability of stoppers with a number of matching threaded couplings. This is an impractical requirement.
Further, systems of this general type normally also are employed to feed gas into the stopper for various purposes. In the system of EP 0 358 353 A2, after the stopper rod has been screwed into the threaded coupling, it must be guaranteed that sealing surfaces of the stopper and the stopper rod are in sealing contact. However, this is possible only if the longitudinal axis of the threaded coupling and the longitudinal axis of the stopper rod are precisely coaxial. In practical operation, such precise coaxial alignment can be achieved only with difficulty. As a result, leaks can occur. Particularly, during a tightening process of a tightening nut employed in such system, a sealing surface of the stopper rod has a tendency to be moved relative to a sealing surface of the stopper. This is due to the fact that the mating threads of the screw coupling automatically have a certain amount of play. Leaks also can occur due to the different coefficients of thermal expansion of the ceramic material of the stopper and the metal material of the stopper rod. As a result, cracks can form in the ceramic material of the stopper. All such leaks are undesirable.